Spark gap electrode



Dec. 25, 1945. F. R. HENsl-:L 2,391,458

SPARK GAP ELECTRODE Filed March 14, 1944 fag-f IN V EN TOR.

' aifz E Hifel wcznemrw Patented Dec. 25, 19.45

sPAm GAP, Emcmona Franz R. Hensel, Indianapolis,- Ind., assigner P. R.Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware v vApplication March 14, 1944, serial 10,526,350

s claims. (ci. 12a-169) This invention relates to improvements `in sparkgap electrodes and more particularly to metallic electrodes suitable foruse in spark plugs, ignition systems, high frequency generators, highfrequency induction furnaces, etc.

Objects of the invention are: to provide elece trical spark gapelectrodes having improved operating characteristics, as well as toprovide .a composition from which such electrodes may be formed.

A more specific object of the invention is to provide metallic materialswhich have, due to the structural composition thereof, more resistanceto pitting and metal transfer during operation, which are lesssusceptible to oxidation, and which operate in an improved manner, ascompared with materials heretofore used in the same fields ofapplication.

Other objects will in part be obvious and will in part appearhereinafter from the following description taken in connection with theaccompanying drawing in which:

Figure 1 illustrates a side view partly in sectionof the invention asapplied to a spark plug electrode;

Figure 2 shows a modified form of electrode, and

Figure 3 shows an end view of Figure 1.'

The invention accordingly comprises improved products possessing thefeatures and properties which will be exemplified in the embodimentshereinafter described and the scope of the application of which will beindicated in the claims.

Many different types of materials have been proposed heretofore for usein spark plug electrodes and similar electrodes subjected to severeoxidizing and/or corrosive atmospheres and/or other deleteriousinfluences. Of the materials used heretofore, either singly or incombination with other metals, tungsten and platinum are among the mostconspicuous. However, these materials suffer from a number ofdisadvantages Which are not encountered in a more recent member of thegroup of refractory or precious metals, namely rhenium, and thisinvention, therefore, contemplates 'the use of rhenium in spark gapelectrodes such asspark plug electrodes, for example.

Comparative tests which were carried out by heating rhenium and tungstenWires, in air at 1000 C., indicated that rhenium Wire possessesconsiderably higher heat and oxidation resistance than tungsten `Wire,the rhenium wire having a useful life about three times as long as thatof the tungsten wire. Similar tests were carried out with a mixture` of`air and nitrogen, the oxygen content .being approximately 10%. In thismixture, rhenium could be heated to 1600 C. before oxidation'started-and the rate of oxldatio was only one-third that of tungsten. f

In hydrogen atmospheres containing a 'small percentage of water vapor,rhenium wires were extremely stable up to the highest temperatures,whereas tungsten was attacked after a relatively short time. Whenrhenium wire was first heated in moist hydrogen at 2000 C. and then inmoist nitrogen, it was possible to heat therhenium wire in thelattercase up to 2300 C., without any evidence of attack. The wire hadto be heated tov 2500 C. before any deleterious oxidation occurred.-These results appear to lead to the conclusion that rhenium may berendered passive by giving it a heat treatment in moist hydrogen.

The present invention proposes to take advantage of the above findings,by formingv electrodes from at least one of the following materials: (l)solid metallic rhenium; (2) a rhenium-plated rod having a core of one ofthe materials tungsten, molybdenum, or an alloy of tungsten and copper,or tungsten and silver; (3) a rhenium-plated rod having a core of amaterial consisting of molybdenum about 5%, copper or nickel about 5%,and the remainder tungsten plus rhenium; (4) rhenium-base compositionsor alloys containing platinum group metals such as ruthenium, rhodium,

palladium, osmium, iridium and platinum in percentages ranging from 0.5to 49%; y(5) rheniumbase compositions or alloys containing refractorymetals of the group comprising tungsten, molybdenum and tantalum inpercentages ranging from .0.5 to 49%; (6) a rhenium composition or alloyof high density produced by creating a liquid phase during sintering.'I'he elements producing such a liquid phase may be either nickel andcopper or low melting point eutectic compositions of molybdenum with aniron-base metal such as nickel, iron or cobalt. Usually the rheniumcontent of such compositions will vary from 'l0 to the balance being themetals constituting the low melting point phase.

Referring to the drawing, Figure l shows an embodiment of the inventionas applied to the construction of a, spark plug, only that portionthereof which is shown in longitudinal section being a part of thisinvention. As shown, the spark plug comprises an insulator I 0 formed ofconventional insulating materials such as a ceramic composition, saidinsulator surrounding the central electrode which comprises an upperportion Il made 0f any suitable metallic composition used heretofore,and a lower section I! which according to this invention may be made ofsolid metallic rhenium or any of the materials set forth under 4, 5 and6 above. The side electrode I5 may be formed of rhenium or rhenium-baseor rhenium-plated material as de scribed above, or of any other suitablematerial.

In the modiiled embodiment of the invention which is shown in Figure 2,the central electrode may comprise a core 20 upon which has been plateda sheath 24 of rhenium. The core 20 may be formed of any of thematerials set forth under 2 or 3 above.

Figure 8 shows a bottom end view of the .spark plug construction ofFigure 1, i2 being the centrai electrode and I5 being the sideelectrode.

The method per se of eiecting the electrodeposition of metallic rheniumupon the spark gap core materials is not a Dart of the present inventionsince a suitable plating method has been described and claimed in U. S.Patent 2,138,573, patented November 29, 1938, to C. G. Fink and PincusDeren. By using the method disclosed in said patent, bright and harddeposits of rhenium metal may be obtained from various aqueous solutionsof rhenium. Rhenium electro-plates readily and rapidly, and its platingsolutions have a good throwing power and give good current eillciencies.Plates of any desired thickness may be easily obtained, and the platesare extremely resistant to attack by oxidizing and corrosive gases athigh temperatures, i. e., under conditions such as are encountered inthe use of spark gap and spark plug electrodes. If desired, rhenium maybe co-deposited upon the core of an electrode or similar member with ametal or metals such as nickel and cobalt.

While the present invention, as toits objects and advantages, has beendescribed herein al carried out in a specific embodiment thereof, theinvention is not to be limited thereby but is intended to be coveredbroadly within the spirit and scope of the appended claims.

What is claimed is:

l. A spark gap electrode containing rhenium.

2. A spark plug electrode composed entirely of metallic rhenium.

3. A spark gap electrode, at least the working surface portion of whichis composed predominantly of rhenium.

4. A spark gap electrode having a body of refractory metal and a workingsurface layer inte- Iglliral therewith composed predominantly of rhe- 5.A spark gap electrode having a, body of refractory metal and a workingsurface layer integral therewith composed of rhenium.

6. A spark gap electrode having a core formed of a refractory metalcomposition and a working face layer formed of rhenium.

7. A spark gap electrode having a core formed of a. refractory metalcomposition and a working ,face layer thereon formed of electrodepositedrhenium.

8. A spark gap electrode, at least the working

